The present invention relates to an integrated circuit device. In particular, this invention relates to an integrated circuit device for fluid ejection. The invention has broad applications to such devices as micro-electromechanical pumps and micro-electromechanical movers.
Micro-electromechanical devices are becoming increasingly popular and normally involve the creation of devices on the micron scale utilizing semi-conductor fabrication techniques. For a review on micro-electromechanical devices, reference is made to the article xe2x80x9cThe Broad Sweep of Integrated Micro Systemsxe2x80x9d by S. Tom Picraux and Paul J. McWhorter published December 1998 in IEEE Spectrum at pages 24 to 33.
One form of micro-electromechanical device is an ink jet printing device in which ink is ejected from an ink ejection nozzle chamber.
Many different techniques on ink jet printing and associated devices have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207 to 220 (1988).
Recently, a new form of ink jet printing has been developed by the present applicant that uses micro-electromechanical technology. In one form, ink is ejected from an ink ejection nozzle chamber utilizing an electromechanical actuator connected to a paddle or plunger which moves towards the ejection nozzle of the chamber for ejection of drops of ink from the ejection nozzle chamber.
The present invention concerns, but is not limited to, an integrated circuit device that incorporates improvements to an electromechanical bend actuator for use with the technology developed by the Applicant.
According to a first aspect of the invention, there is provided a fluid ejection device which comprises
a substrate;
nozzle chamber walls arranged on the substrate and defining a plurality of nozzle chambers, the substrate defining a plurality of fluid inlet channels in fluid communication with the nozzle chambers to supply fluid to the nozzle chambers;
drive circuitry arranged on the substrate; and
a plurality of micro-electromechanical devices positioned on the substrate, each device comprising:
an elongate actuator having a fixed end that is fast with the substrate so that the actuator is connected to the drive circuitry and a working end that is displaceable along a path relative to the substrate to perform work, the actuator including a pair of elongate arms that are spaced relative to each other along the path and are connected to each other at each end, with one of the arms being connected to the drive circuitry to define a heating circuit and being of a material that is capable of expansion when heated, such that, when the heating circuit receives an electrical signal from the drive circuitry, that arm expands relative to the other to deform the actuator and thus displace said working end along said path; and
a fluid displacement member that is fixed to the working end of the elongate actuator and is positioned in a respective nozzle chamber so that displacement of the working end and thus the fluid displacement member results in the ejection of fluid from the nozzle chamber.
The nozzle chamber walls include roof walls that define fluid ejection ports, each fluid displacement member being displaceable towards and away from a respective fluid ejection port to eject fluid from that ejection port.
Each nozzle chamber wall may define an opening to accommodate a respective actuator, the nozzle chamber wall and the actuator being configured so that, when the nozzle chamber is filled with fluid, surface tension effects of the fluid establish a fluidic seal between the actuator and the nozzle chamber wall.
The substrate may define a recess about each nozzle chamber wall to inhibit picking of fluid across the substrate.
Each fluid displacement member may be in the form of a paddle member that spans a region between the respective nozzle chamber and the respective fluid inlet channel so that, when the heating circuit receives a signal from the drive circuitry, the paddle member is driven towards the fluid ejection port and fluid is drawn into the respective nozzle chamber.
Each paddle member may have a projecting formation positioned on a periphery of the paddle member, the formation projecting towards the ejection port so that the efficacy of the paddle member can be maintained while inhibiting contact between the paddle member and a meniscus forming across the ejection port.
Each actuator may include a heat sink that is positioned on the arm that defines the heating circuit, intermediate ends of that arm, to provide generally uniform heating along the length of the arm.
Each actuator may include at least one strut that is fast with each arm at a position intermediate ends of the arms.
According to a second aspect of the invention, there is provided a mechanical actuator for micro mechanical or micro electromechanical devices, the actuator comprising:
a supporting substrate;
an actuation portion;
a first arm attached at a first end thereof to the substrate and at a second end to the actuation portion, the first arm being arranged, in use, to be conductively heated;
a second arm attached at a first end to the supporting substrate and at a second end to the actuation portion, the second arm being spaced apart from the first arm, whereby the first and second arms define a gap between them;
at least one strut interconnecting the first and second arms between the first and second ends thereof; and
wherein, in use, the first arm is arranged to undergo expansion, thereby causing the actuator to apply a force to the actuation portion.
Preferably the first arm includes a first main body formed between the first and second ends of the first arm. Preferably the second arm includes a second main body formed between the first and second ends of the second arm. A second tab may extend from the second main body. The first one of the at least one strut may interconnect the first and second tabs.
Preferably the first and second tabs extend from respective thinned portions of the first and second main bodies.
Preferably the first arm includes a conductive layer that is conductively heated to cause, in use, the first arm to undergo thermal expansion relative to the second arm thereby to cause the actuator to apply a force to the actuation portion.
Preferably the first and second arms are substantially parallel and the strut is substantially perpendicular to the first and second arms.
Preferably a current is supplied in use, to the conductive layer through the supporting substrate.
Preferably the first and second arms are formed from substantially the same material. Preferably the actuator is manufactured by the steps of:
depositing and etching a first layer to form the first arm;
depositing and etching a second layer to form a sacrificial layer supporting structure over the first arm;
depositing and etching a third layer to form the second arm; and
etching the sacrificial layer to form the gap between the first and second arms.
Preferably the first arm includes two first elongated flexible strips conductively interconnected at the second arm. Preferably the second arm includes two second elongated flexible strips. Preferably the actuation portion comprises a paddle structure.
Preferably the first arm is formed from titanium nitride. Preferably the second arm is formed from titanium nitride.